1. Field of the Invention
The present invention relates to an apparatus for the intensive degassing of polyvinyl chloride-containing dispersions, essentially comprising a polymerization reactor (1), a cooling device (2), and a vacuum unit (3), where the polymerization reactor (1) contains a steam inlet (4) in the lower half, and the polymerization reactor (1), the cooling device (2) and the vacuum unit (3) are connected to one another via a connector (5).
The present invention furthermore relates to the use of the novel apparatus for the intensive degassing of PVC dispersions, and to a process for this purpose.
2. Description of the Prior Art
DE-A 25 31 111 describes a process for the removal of residual vinyl chloride (VC) from vinyl chloride polymer in aqueous dispersion (both suspension and emulsion), where the aqueous dispersion of the polymer is brought to a temperature at least the same as the freezing range of the polymer and is subjected to entrainment by an inert fluid. In particular, DE-A 25 31 111 uses steam as the inert fluid, which, after leaving the aqueous dispersion, is condensed in a condenser, on which a vacuum pump is arranged directly. The disadvantage of this process are the residual VC values in the degassed suspensions (in contrast to emulsions, which naturally can be degassed more easily owing to their particle size). According to the table in DE-A 25 31 111, the residual VC contents before drying are not less than 25 ppm. The value given for Example 5 corresponds to the residual VC content after drying, since the same conditions as in Example 1 were observed apart from a shorter (!) degassing time.
EP-A 359 432 describes an apparatus for degassing liquid mixtures essentially comprising polystyrene and volatile constituents such as monomers, in which a heat exchanger and a vacuum unit are connected directly to the vessel containing the polymer mixture to be degassed. The residual monomer contents achieved are less than 300 ppm, but are not below 177 ppm.